The invention relates to a solution of an alkali salt, which is strongly basic, clear, stable in storage and liquid at room temperature, of aniline, which is amidated with a monocarboxylic acid, or its derivatives in an aprotic solvation agent, a method for production thereof and the polyamides produced with this solution.
Various developments have become known recently for accelerated anionic lactam polymerisation, which use so-called liquid systems in order to initiate the lactam polymerisation. A liquid multi-component system of this type for the implementation of anionic lactam polymerisation is described in DE 196 03 305 C2. This system essentially comprises sodium caprolactamate which contains lactam-acylating compounds and solvation agents.
It has thereby been shown that systems of this type have only a limited storage life.
A liquid system is likewise described in WO 01/46293 A1 which, in contrast to the system of DE 196 03 305 C2, is lactam-free. This liquid system thereby contains a conversion product of isocyanate with a protic compound and a base in an aprotic solvation agent. It has been shown that this solution has in fact improved stability in storage relative to the solutions known to date in the state of the art, however it has been established with these liquid systems that they always exhibit discolouration to various extents. It is hereby particularly unfavourable that, when storing these solutions, this discolouration is intensified and, when this solution is used, the result can be discolouration of the produced polyamides.
Starting herefrom, it is therefore the object of the present invention to make available an improved liquid system for anionic lactam polymerisation which, in addition to good stability in storage, has an invariable inherent colour which remains constant also for the duration of the storage. The liquid system should furthermore be easily producible and environmentally safe. A further object of the invention is to indicate a method for producing systems of this type and the polyamides produced with the liquid system.